1. Field of the Invention
The present invention generally relates to a method for producing a metal/ceramic bonding circuit board wherein a metal circuit plate is bonded to a ceramic substrate. More specifically, the invention relates to a method for producing a metal/ceramic bonding circuit board for use in a power module or the like.
2. Description of the Prior Art
As a conventional method for producing a metal/ceramic bonding circuit board for use in a power module or the like, there is known a method for producing a metal/ceramic bonding circuit board which has a metal circuit plate having a desired circuit pattern, the method comprising the steps of: cooling and solidifying a molten metal, which is fed onto a ceramic substrate, to bond a metal plate to the ceramic substrate; printing an etching resist having a desired pattern shape on the bonded metal plate by the screen printing or the like; etching the metal plate to form a circuit pattern; and removing the resist (see, e.g., Japanese Patent Laid-Open No. 2002-76551).
However, in a typical metal/ceramic bonding circuit board for use in a power module or the like, the thickness of a metal circuit plate is not less than hundreds micrometers, and is tens times as large as the thickness of a metal circuit plate of a printed circuit board usually using a paper or glass epoxy as an insulating material. Therefore, in the method disclosed in Japanese Patent Laid-Open No. 2002-76551, there is a problem in that the length of a skirt formed by etching and the amount of side etching caused by etching are large. For example, if the thickness of a metal circuit plate is in the range of from 0.4 mm to 0.6 mm and if an etching resist having a distance between patterns of 0.5 mm is formed, the insulating distance between patterns (the distance between bottoms) of the metal plate is a great distance of 0.9 to 1.4 mm at the shortest, and the distance between tops of metal circuit plates is greater than the distance between bottoms. If the metal circuit plate is thicker, there is a problem in that these distances are greater. In addition, as the thickness of the metal circuit plate increases, the time required to carry out etching increases, and the number of producing steps increases to increase production costs. Moreover, the resistance of the etching resist must be cared.